Solar Array Drive Mechanisms (SADM)

SADM

Most of the three-axis stabilized satellites use solar panels to generate the necessary electrical power for their equipments. For better performances, these panels have to be aligned continuously such as to get normal incident sun light onto the solar cells. In most of the cases, when the satellite’s body is pointing towards a defined target and its orientation is not more fixed with respect to the sun, a relative motion between the satellite’s body and the solar panels must be provided. The rotating mechanism performing this task is the Solar Array Drive Mechanism (SADM). A SADM acts as the solar array motor and electrical power (and data) transfer between the solar arrays and spacecraft body being then under relative motion. A motor is used to rotate the solar array at the required speed and in the required direction, and a specific electrical device (slip-ring, cable-wrap, twisted capsule, etc …) is used to transfer the power (and data) between the solar array and the satellite.

The SADM is one of the very critical hardware of a spacecraft (Single Point Failure) and its design is usually optimised with respect to the specific satellite platform and its power needs that can nowadays cover a wide range from ~500W to ~20000W per Solar Array wing. It exists therefore a numerous types of SADM on the market.

Typical main and secondary functions of a SADM are as follows:

To mechanically link the solar array to the satellite

To maintain the solar array along one specific satellite’s axis

To allow for the solar array to rotate around one specific satellite’s axis

To point the solar array towards the sun

To rotate the solar array at nominal speed (via SADE or satellite command)

To rotate the solar array into a reference position (via SADE or satellite command)

To rotate the solar array in a high-speed mode (via SADE or satellite command)

To maintain the solar array in a defined/fixed position (via SADE or satellite command)

To provide telemetry signals from the SADM (incl. SADM angular position sensor)

To transfer the solar array electrical power to the satellite

To transfer signals and low power lines between the “rotating” part (solar array side) and the “fixed” part of the satellite (platform)